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LTC3589_12 Datasheet, PDF (22/50 Pages) Linear Technology – 8-Output Regulator with Sequencing and I2C | |||
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LTC3589/LTC3589-1/
LTC3589-2
OPERATION
while powering up following a fault condition. A soft-start
cycle is not triggered by a change of operating modes or
a dynamic voltage slew. During soft-start the converter is
forced to pulse-skipping mode regardless of the settings
in the SCR1 command register.
Table 6. Step-Down Switching Regulator 2 Command Register
Settings
COMMAND
VALUE SETTING
REGISTER[BIT]
SCR1[3-2]
00* Pulse-Skipping Mode
01 Burst Mode Operation
10 Forced Continuous Mode
OVEN[1]
0* Disable
1 Enable
SCR2[1]
0* Wait for Output Below 300mV Before Enable
LTC3589/LTC3589-1 1 Enable immediately
SCR2[1]
LTC3589-2
0* Enable immediately
1 Wait for Output Below 300mV Before Enable
VCCR[3]
0* Select Register B2DTV1 (V1) Reference
1 Select Register B2DTV2 (V2) Reference
VCCR[2]
1 Initiate Dynamic Voltage Slew
VRRCR[3-2]
00 Reference Slew Rate = 0.88mV/μs
01 Reference Slew Rate = 1.75mV/μs
10 Reference Slew Rate = 3.5mV/μs
11* Reference Slew Rate = 7mV/μs
B2DTV1[5]
0* Force PGOOD Low When Slewing
1 Normal PGOOD Operation When Slewing
B2DTV1[4-0]
11001* DAC Dynamic Target Voltage V1
B2DTV2[4-0]
11001* DAC Dynamic Target Voltage V2
B2DTV2[5]
0* 2.25MHz Switching Frequency
1 1.125MHz Switching Frequency
B2DTV2[6]
0* Switch on Clock Phase 1
1 Switch on Clock Phase 2
B2DTV2[7]
0* Shutdown Regulator 2 Normally
1 Keep Regulator 2 Alive
* Denotes Default Power-On Value
Switching EMI Control
The step-down switching regulators contain new pat-
ent pending circuitry to limit the edge rate of the switch
nodes SW1, SW2, and SW3. This new circuitry controls
the transition of the switch node over a period of a few
nanoseconds, signiï¬cantly reducing radiated EMI and
conducted supply noise while maintaining high efï¬ciency.
Since slowing the slew rate of the switch nodes causes
efï¬ciency loss, the slew rate of the step-down switching
regulators is adjustable using the I2C command register
B1DTV1 bits 6 and 7. Optimize efï¬ciency or EMI as neces-
sary with four different slew rate settings. The power-on
default is the fastest slew rate, highest efï¬ciency setting.
Table 7. Step-Down Switching Regulator 3 Command Register
Settings
COMMAND
VALUE SETTING
REGISTER[BIT]
SCR1[5-4]
00* Pulse-Skipping Mode
01 Burst Mode Operation
10 Forced Continuous Mode
OVEN[2]
0* Disable
1 Enable
SCR2[2]
0* Wait for Output Below 300mV Before Enable
LTC3589/LTC3589-1 1 Enable Immediately
SCR2[2]
LTC3589-2
0* Enable Immediately
1 Wait for Output Below 300mV Before Enable
VCCR[5]
0* Select Register B3DTV1 (V1) Reference
1 Select Register B3DTV2 (V2) Reference
VCCR[4]
1 Initiate Dynamic Voltage Slew
VRRCR[5-4]
00 Reference Slew Rate = 0.88mV/μs
01 Reference Slew Rate = 1.75mV/μs
10 Reference Slew Rate = 3.5mV/μs
11* Reference Slew Rate = 7mV/μs
B3DTV1[5]
0* Force PGOOD Low When Slewing
1 Normal PGOOD Operation When Slewing
B3DTV1[4-0]
11001* DAC Dynamic Target Voltage V1
B3DTV2[4-0]
11001* DAC Dynamic Target Voltage V2
B3DTV2[5]
0* 2.25MHz Switching Frequency
1 1.125MHz Switching Frequency
B3DTV2[6]
0* Switch on Clock Phase 1
1 Switch on Clock Phase 2
B3DTV2[7]
0* Shutdown Regulator 3 Normally
1 Keep Regulator 3 Alive
* Denotes Default Power-On Value
Operating Frequency
The switching frequency of each of the LTC3589 step-
down switching regulators may be independently set using
I2C command register bits B1DTV2[5], B2DTV2[5] and
B3DTV2[5]. The power-on default frequency is 2.25MHz.
Writing bit BxDTV2[5] HIGH will reduce the switching fre-
3589fe
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